Rotary blood pump

ABSTRACT

Various “contactless” bearing mechanisms including hydrodynamic, hydrostatic, and magnetic bearings are provided for a rotary pump as alternatives to mechanical contact bearings. These design features may be combined. In one embodiment, a pump housing has a spindle extending from a wall of the pump housing into a pumping chamber defined by the pump housing. The spindle has a stepped portion adjacent the wall. In one embodiment, the stepped portion is defined by a change in spindle diameter. The lack of mechanical contact bearings enables longer life pump operation and less damage to working fluids such as blood.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/504,233 of Wampler, et al. filed Sep. 18, 2003.

FIELD OF THE INVENTION

This invention relates to the field of rotary pumps. In particular, thisinvention is drawn to bearings for various rotor and impellerarchitectures.

BACKGROUND OF THE INVENTION

Typical rotary pumps utilize an impeller wherein the movement of theimpeller is constrained in five degrees of freedom (two angular, threetranslational) by mechanical contact bearings. Some working fluids maybe damaged by the mechanical contact bearings. Blood pumped throughpumps with contact bearings can experience hemolysis, i.e., damage toblood cells. In general, a hydraulically efficient and power efficientpump that can handle delicate working fluids such as blood is desirablefor some applications.

U.S. Pat. No. 6,234,772 B1 of Wampler, et al., (“Wampler”) describes acentrifugal blood pump having a repulsive radial magnetic bearing and anaxial hydrodynamic bearing. U.S. Pat. No. 6,250,880 B1 of Woodard, etal. (“Woodard”) describes a centrifugal blood pump with an impellersupported exclusively by hydrodynamic forces.

Both blood pumps are based on an axial flux gap motor design. The pumpimpeller carries the motor drive magnets thus serving as a motor rotor.In both cases, the drive magnets are disposed within the blades of theimpeller. Drive windings reside outside the pump chamber but within thepump housing that serves as the motor stator. Integration of the motorand pump enables the elimination of drive shafts and seals for thepumps. The pump/motors include a back iron to increase the magnetic fluxfor driving the impeller.

Both blood pumps suffer from hydraulic inefficiencies due at least inpart to the large, unconventional blade geometry required for disposingthe magnets within the impeller blades.

The natural attraction between the magnets carried by the impeller andthe back iron creates significant axial forces that must be overcome inorder for the pump to work efficiently. Hydrodynamic bearings can damageblood cells as a result of shear forces related to the load carried bythe hydrodynamic bearings despite the lack of contact between theimpeller and the pump housing. Thus exclusive reliance on hydrodynamicbearings may be harmful to the blood.

SUMMARY OF THE INVENTION

In view of limitations of known systems and methods, various“contactless” bearing mechanisms are provided for a rotary pump asalternatives to mechanical contact bearings. Various rotor and housingdesign features are provided to achieve hydrodynamic, hydrostatic, ormagnetic bearings. These design features may be combined. The lack ofmechanical contact bearings enables longer life pump operation and lessdamage to working fluids such as blood.

In one embodiment, a pump includes a pump housing defining a pumpingchamber. The pump housing has a spindle extending into the pumpingchamber. The spindle further comprises an upper spindle magnet and alower spindle magnet. A rotor configured to rotate about the spindle hasan upper rotor magnet and a lower rotor magnet. The upper spindle androtor magnets are arranged to repel each other. The lower spindle androtor magnets are arranged to repel each other.

In one embodiment, the pump includes a hydrostatic thrust bearing. Thepump housing has a spindle extending from a wall of the pump housinginto the pumping chamber defined by the pump housing. The spindle has astepped portion adjacent the wall. In one embodiment, the steppedportion is defined by a change in spindle diameter.

In various embodiments, the rotor includes either paddles or groovesdisposed about the periphery of the rotor. The rotor may include agrooved bore. The grooved bore may be combined with the grooved orpaddled periphery. The paddles and grooves generate a hydrostatic thrustforces during rotation of the rotor.

The pump may include both the hydrostatic and magnetic thrust bearings.In addition, the pump may incorporate a hydrodynamic thrust or ahydrodynamic radial bearing, or both.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 illustrates a cross-section of a pump having a passive magneticaxial bearing.

FIG. 2 illustrates one embodiment of the passive magnetic axial bearing.

FIG. 3 illustrates center and off-center placement of the passivemagnetic axial bearing.

FIG. 4 illustrates one embodiment of a passive magnetic repulsive axialbearing.

FIG. 5 illustrates one embodiment of a passive magnetic repulsive axialbearing.

FIG. 6 illustrates an axial hydrostatic bearing in a first position.

FIG. 7 illustrates an axial hydrostatic bearing in a second position.

FIG. 8 illustrates one embodiment of an impeller.

FIG. 9 illustrates an alternative embodiment of an impeller with groovedsurfaces for creating a hydrostatic bearing.

FIG. 10 illustrates an alternative embodiment of an impeller with bladedsurfaces for creating a hydrostatic bearing.

FIGS. 11A and 11B illustrate embodiments of grooved surfaces forcreating hydrostatic bearings.

FIG. 12 illustrates one embodiment of the pump used in a medicalapplication.

DETAILED DESCRIPTION

FIG. 1 illustrates one embodiment of a centrifugal blood pump. The pumpcomprises a housing 110 defining a pumping chamber 112 between an inlet114 and an outlet 116. Within the pumping chamber, a rotor 120 rotatesabout a spindle 130 protruding from a base of the pump housing. Therotor further comprises a bladed portion defining an impeller thatprovides the fluid moving surfaces. The impeller comprises one or moreblades 121 that move fluids when the impeller rotates.

The terms “rotor” and “impeller” may be used interchangeably in somecontexts. For example, when the rotor is rotating, the blade portion ofthe rotor is inherently rotating such that reference to rotation ofeither the impeller or the rotor is sufficient to describe both. Whennecessary, however, the term “non-bladed portion of the rotor” or “rotorexcluding the impeller” may be used to specifically identify portions ofthe rotor other than the blades. Each blade of the rotor may separatelybe referred to as an impeller, however the term “impeller” is generallyused to refer to a collective set of one or more blades.

The pump is based upon a moving magnet axial flux gap motorarchitecture. In one embodiment, the motor is a brushless DC motor.Drive magnets 122 carried by the rotor have magnetic vectors parallel tothe rotor axis of rotation 190. In the illustrated embodiment, the drivemagnets are disposed within a non-bladed portion of the rotor.

Drive windings 140 are located within the pump housing. Power is appliedto the drive windings to generate the appropriate time-varying currentsthat interact with the drive magnets in order to cause the impeller torotate. A back iron 150 enhances the magnetic flux produced by the motorrotor magnets. In one embodiment, either the face 124 of the bottom ofthe rotor or the opposing face 118 provided by the lower pump housinghave surfaces (e.g., 172) contoured to produce a hydrodynamic bearingwhen the clearance between the rotor and the housing falls below apre-determined threshold. In one embodiment, the pre-determinedthreshold is within a range of 0.0002 inches to 0.003 inches.

The natural attraction between the back iron 150 and the drive magnets122 carried by the rotor can create a significant axial load on therotor. This axial load is present in centrifugal pumps based on an axialflux gap motor architecture such as Wampler or Woodard. Woodard andWampler both rely on hydrodynamic thrust bearings to overcome this axialloading force. Despite the lack of contact, hydrodynamic bearings canstill damage blood cells as a result of shear forces related to the loadcarried by the hydrodynamic bearings.

The repulsive radial magnetic bearing of Wampler exacerbates the axialloads created by the magnetic attraction between the drive magnets andthe back iron. Although the repulsive radial magnetic bearing createsradial stability, it introduces considerable axial instability. Thisaxial instability can contribute further to the axial loading. Thisadditional axial loading creates greater shear forces for any axialhydrodynamic bearing that can cause undesirable hemolysis for bloodapplications. In addition, the power required to sustain thehydrodynamic bearing increases as the load increases. Thus highly loadedhydrodynamic bearings can impose a significant power penalty.

The blood pump of FIG. 1 includes a magnetic axial bearing that servesto reduce or offset the axial load imposed on the rotor by theinteraction between the drive magnets and the back iron. The axialmagnetic bearing is formed by the interaction between a spindle magnetassembly 160 disposed within the spindle and a rotor magnet assembly 180carried by the rotor. In the illustrated embodiment, the rotor magnetassembly 180 is disposed proximate the impeller, but the magnets of therotor magnet assembly are not located within the blades. A set screw 134permits longitudinal adjustment of the axial position of the axialmagnetic bearing by moving the spindle magnet assembly along alongitudinal axis of the spindle.

FIG. 2 illustrates one embodiment of the axial magnetic bearing. Therotor magnet assembly includes a first rotor bearing magnet 282 and asecond rotor bearing magnet 284 proximately disposed to each other. Thefirst and second rotor bearing magnets are permanent magnets. In oneembodiment, a pole piece 286 is disposed between them. A pole piece orflux concentrator serves to concentrate the magnetic flux produced byrotor bearing magnets 282 and 284. In an alternative embodiment, element286 is merely a spacer to aid in positioning the first and secondbearing magnets 282, 284 and does not serve to concentrate any magneticflux. In other embodiments, element 286 is omitted so that the rotormagnet assembly does not include a spacer or a pole piece element.

In one embodiment, elements 282 and 284 are monolithic, ring-shapedpermanent magnets (see, e.g., 250 (a)). In alternative embodiments, thebearing magnets may be non-monolithic compositions (see, e.g,. 250 (b),(c), (d)). For example, a bearing magnet may be composed of a pluralityof pie-shaped, or arcuate segment-shaped (250 (b)), or other shapes (250(c), (d)) of permanent magnet elements that collectively form aring-shaped permanent magnet structure.

The rotor axial bearing magnet assembly is distinct from the drivemagnets 222 carried by a portion of the rotor other than the blades 221.In the illustrated embodiment, the drive magnets are disposed within thenon-bladed portion 228 of the rotor.

The spindle magnet assembly includes a first spindle bearing magnet 262and a second spindle bearing magnet 264. The first and second spindlebearing magnets are permanent magnets. In one embodiment, a pole piece266 is disposed between them. Pole piece 266 concentrates the magneticflux produced by the spindle bearing magnets 262 and 264. In analternative embodiment, element 266 is merely a spacer for positioningthe first and second spindle bearing magnets and does not serve toconcentrate any magnetic flux. In other embodiments, element 266 isomitted so that the spindle magnet assembly does not include a spacer ora pole piece element.

In the illustrated embodiment, permanent magnets 262 and 264 arecylindrical. Other shapes may be utilized in alternative embodiments.The ring-shaped rotor magnets rotate with the impeller about alongitudinal axis of the spindle that is shared by the spindle bearingmagnet assembly.

The permanent magnets of each of the spindle and rotor bearingassemblies are arranged such that the magnetic vectors of the individualmagnets on either side of the intervening pole pieces oppose each other.Each side of a given pole piece is adjacent the same pole of differentmagnets. Thus the magnetic vectors of magnets 262 and 264 oppose eachother (e.g., N-to-N or S-to-S). Similarly, the magnetic vectors ofmagnets 282 and 284 oppose each other.

The orientation of the magnets is chosen to establish an axialattraction whenever the bearings are axially misaligned. Note that therelative orientations of the spindle and rotor magnet assemblies areselected so that the spindle and rotor magnet assemblies attract eachother (e.g., S-to-N, N-to-S). The magnet vector orientation selected forthe magnets of one assembly determines the magnetic vector orientationfor the magnets of the other assembly. Table 292 illustrates theacceptable magnetic vector combinations for the first and second rotorbearing magnets (MR1, MR2) and the first and second spindle bearingmagnets (MS1, MS2). Forces such as the magnetic attraction between theback iron and drive magnets that tend to axially displace the magnetbearing assemblies are offset at least in part by the magneticattraction between the axial bearings that provide an axial force torestore the axial position of the rotor.

FIG. 2 also illustrates wedges or tapered surfaces 272 that form aportion of a hydrodynamic bearing when the clearance between a face ofthe non-bladed portion of the rotor (see, e.g., bottom face 124 ofFIG. 1) and the back of the pump housing falls below a pre-determinedthreshold. In various embodiments, this pre-determined threshold iswithin a range of 0.0002 inches to 0.003 inches. Thus in one embodiment,the pump includes an axial hydrodynamic bearing. The surface geometryproviding the axial hydrodynamic bearing may be located on the rotor orthe housing.

Although the spindle magnet assembly is intended to provide an axialmagnetic bearing, the attractive force between the spindle and rotormagnet assemblies also has a radial component. This radial component maybe utilized to offset radial loading of the impeller due to the pressuregradient across the impeller. The radial component also serves as apre-load during initial rotation and a bias during normal operation toprevent eccentric rotation of the rotor about the spindle. Such aneccentric rotation can result in fluid whirl or whip which isdetrimental to the pumping action. The biasing radial component helps tomaintain or restore the radial position of the rotor and the pumpingaction, for example, when the pump is subjected to external forces as aresult of movement or impact.

Instead of a spindle magnet assembly interacting with a rotor bearingmagnet assembly to form the magnetic bearing, a ferromagnetic materialmight be used in lieu of one of a) the spindle magnet assembly, or b)the rotor bearing magnet assembly (but not both) in alternativeembodiments.

The alternative magnetic bearing is still composed of a spindle portionand a rotor portion, however, one of the spindle and the rotor portionsutilizes ferromagnetic material while the other portion utilizespermanent magnets. The ferromagnetic material interacts with the magnetsto create a magnetic attraction between the rotor and spindle. Examplesof ferromagnetic materials includes iron, nickel, and cobalt.

In one embodiment, the ferromagnetic material is “soft iron”. Soft ironis characterized in part by a very low coercivity. Thus irrespective ofits remanence or retentivity, soft iron is readily magnetized (orre-magnetized) in the presence of an external magnetic field such asthose provided by the permanent magnets of the magnetic bearing system.

FIG. 3 illustrates various locations for the placement of the spindleportion of the magnetic bearing. In one embodiment, the spindle magnetassembly 360 is axially aligned with a longitudinal axis 390 of thespindle so that the spindle and spindle magnet assembly share the samecentral longitudinal axis. In an alternative embodiment, the spindlemagnet assembly is radially offset so that the spindle and spindlemagnet assembly do not share the same central axis. In particular, thelongitudinal axis 362 of the spindle magnet assembly 360 is displacedfrom the longitudinal axis 390 of the spindle. This latter positioningmay be desirable to provide some radial biasing force. A difference inpressure across the impeller tends to push the impeller radially towardsone side of the pump housing. This radial load may be offset at least inpart by offsetting the spindle magnet assembly.

Although the spindle and rotor magnet assemblies are illustrated ascomprising 2 magnetic elements each, the magnet assemblies may eachcomprise a single magnet instead. A greater spring rate may be achievedwith multiple magnetic elements per assembly configured as illustratedinstead of a single magnet per assembly. The use of two magneticelements per assembly results in a bearing that tends to correctbi-directional axial displacements from a position of stability (i.e.,displacements above and below the point of stability) with a greaterspring rate than single magnetic elements per assembly.

FIG. 4 illustrates an alternative axial magnetic bearing. The axialmagnetic bearing is based upon axially repulsive magnetic forcesgenerated between the rotor 420 and the spindle 430. The axial magneticbearing is formed from opposing upper magnets in the rotor and spindleand opposing lower magnets in the rotor and spindle.

In the illustrated embodiment, the rotor includes one or more upperbearing magnetic elements 482 and one or more lower bearing magneticelements 484. The spindle includes one or more upper bearing magneticelements 462 and one or more lower bearing magnetic elements 464. Thespindle and rotor upper bearing magnet elements (462, 482) arepositioned so that their respective magnetic vectors oppose each otheras illustrated. Similarly, the spindle and rotor lower bearing magnetelements (464, 484) are positioned so that their respective magneticvectors oppose each other as illustrated.

FIG. 5 illustrates one embodiment of the upper and lower magneticelements forming the upper and lower magnetic bearings in the spindleand rotor. The rotor upper 582 and lower 584 magnetic elements arering-shaped. The upper and lower rings may each be formed from a singlemagnet or a plurality of distinct magnetic elements. The opposingspindle upper 562 and lower 564 magnetic elements are similarlyring-shaped.

The magnetic vectors of the upper rotor and upper spindle bearingmagnets oppose each other. Similarly, the magnetic vectors of the lowerrotor and lower spindle bearing magnets oppose each other. Given thatthere is no magnetic coupling between the upper and lower spindle magnetelements the relative magnetic vector orientation between the upper andlower spindle magnetic elements is irrelevant. Similarly, the relativemagnetic vector orientation between the upper and lower rotor magneticelements is irrelevant. Table 592 sets forth a number of combinationsfor the magnetic vectors of the upper rotor (UR), upper spindle (US),lower rotor (LR), and lower spindle (LS) magnetic elements.

The magnetic force generated by the axial magnetic bearing will exhibita radial component in addition to their axial components. The radialcomponent will tend to de-stabilize the rotor. In particular, the radialcomponent may introduce radial position instability for the magneticbearings of either FIGS. 1 or 4.

This radial instability may be overcome using radial hydrodynamicbearings. Referring to FIG. 4, the pump may be designed for a radialhydrodynamic bearing (i.e., hydrodynamic journal bearing) locatedbetween the spindle 430 and the rotor along the bore of the rotor.Alternatively, the pump may be designed for a radial hydrodynamicbearing located between the periphery 422 of the rotor and the wall 412of the lower portion of housing 410. In one embodiment, the pumpincludes both a radial hydrodynamic bearing (i.e., hydrodynamic journalbearing) in both locations.

The clearances illustrated in FIG. 4 are exaggerated. Hydrodynamicjournal bearings require narrow clearances to be effective. In variousembodiments, the hydrodynamic journal bearing clearances range from0.0005-0.020 inches. Although the pump of FIG. 4 has been provided as anexample, the radial hydrodynamic bearing(s) may similarly beincorporated into the pump of FIG. 1. The surface geometries suitablefor axial (thrust) or radial (journal) hydrodynamic bearings may belocated on either the rotor or on an associated portion of the housing(or spindle). In one embodiment, the surface geometry includes featuressuch as one or more pads (i.e., a feature creating an abrupt change inclearance such as a step of uniform height). In alternative embodiments,the surface geometry includes features such as one or more tapers.

Another type of non-contacting bearing is a hydrostatic bearing. FIGS. 6and 7 illustrate a pump with an axial hydrostatic thrust bearing. Theaxial hydrostatic bearing may be combined with or used in lieu of theaxial magnetic thrust bearings of FIGS. 1-5.

The axial hydrostatic forces are created by the rotor during rotation.Referring to FIGS. 6 and 7, the spindle 630, 730 includes a step 634,734 that serves to regulate the hydrostatic bearing and the axialposition of the rotor.

FIG. 7 illustrates starting conditions for the pump. When the rotor 720rotates, a pressure differential rapidly develops between the area abovethe impeller blades and the area 794 between the blades and lowerhousing. When there is no gap between the step 734 and the rotor, thepressure in area 794 will be greater than the pressure above the bladescreating lift for the rotor. As the rotor lifts away from the lowerhousing, the gap between the step 794 and rotor 720 increases.

Referring to FIG. 6, once the rotor lifts away from the lower housingand the step 634, a pressure relief path becomes available through thebore of the rotor. If the hydrostatic pressure is too great, the rotorwill move away from the lower housing toward the pump inlet 614. Thisincreases gap 694. In the illustrated embodiment, the spindle includes ahead portion that serves as a rotor stop to prevent the rotor fromtranslating too far along the longitudinal axis of the spindle. Thespindle, however, may omit the head portion in an alternativeembodiment.

As the rotor moves towards the lower housing, gap 694 decreases. Thisrestricts the pressure relief path through the bore and allows pressureto start building below the blades again. The step (634, 734) serves asa self-regulating throttle for the axial hydrostatic bearing.

The term “step” refers to a transition in cross-sectional area. In oneembodiment the cross-section is circular. The size of the gap 694 is afunction of the displacement of the rotor from the lower housing and theshape or profile of the step 634 and of the opposing portion 636 of therotor.

Mathematically, the profile of the step may consist of one or morediscontinuities aside from the endpoints defined by the spindle and thehousing. Referring to callout 650, the transition between the spindleand the housing may be continuous (650 (b), (c), (d)). Alternatively,the transition may comprise one (e.g., 650 (a)) or more (e.g., 650 (e))discontinuities. In the illustrated variations, the profile of the stepis monotonic. Any curvature of the profile between discontinuities (orbetween the endpoints) may be concave 650 (b) or convex 650 (c).

The slope of the profile of the step may vary between discontinuities orthe endpoints. Profile 650 (d) for example, corresponds to a conicalstep (i.e., a step formed of a conical frustum). Profile 650 (e)corresponds to a series of stacked conical frustums.

In various embodiments, the profile of the opposing portion 636 of therotor is substantially complementary to the profile of the step 634.Generally in such cases, there is a rotor axial displacement for whichthe gap is substantially constant (see, e.g., profiles (a), (b), (c),and (e)). Alternatively, the opposing portion 636 of the rotor need notbe precisely complementary to the step 634. Thus there may not be arotor axial displacement for which the gap between the step 634 andopposing portion 636 of the rotor is constant (see, e.g., profiles 650(d), (f)). The step and opposing portion of the rotor illustrated inprofile (d), for example, are both generally conical but have differentslopes. Profile 650 (f) illustrates a curved step working in conjunctionwith a conical opposing portion of the rotor.

FIG. 8 illustrates one embodiment of the rotor 800 including animpeller. The rotor 800 includes a plurality of blades 820 used forpumping the working fluid such as blood. The rotor includes a bore 810.The rotor bore is coaxially aligned with the longitudinal axis of thespindle within the pump housing. Drive magnets (not illustrated) aredisposed within the non-bladed portion 830 of the rotor (i.e., withinthe rotor but not within any blades of the impeller portion of therotor). The motor rotor and pump impeller are thus integrated so that adrive shaft is not required. Elimination of the drive shaft also permitselimination of shaft seals for the pump.

FIG. 9 illustrates an alternative embodiment of the rotor. Rotor 900similarly includes a bore 910 and a plurality of pumping blades 920. Therotor includes additional features to create hydrostatic thrust forceswhile rotating. In one embodiment, the rotor has a grooved bore. Inparticular, the bore has one or more helical grooves 950. The boregrooves have a non-zero axial pitch. The groove is in fluidcommunication with the working fluid of the pump during operation of thepump.

Alternatively or in addition to the grooved bore, the rotor includes aplurality of grooves 940 located at a periphery of the rotor. Theperipheral grooves may be located exclusively on the non-bladed portionof the rotor as illustrated in which case the peripheral grooves extendfrom a lower face 922 to an upper face 924 of the rotor. In analternative embodiment, the peripheral grooves extend from the lowerface 922 to the top of the blades 920 as indicated by groove 942. Theperipheral grooves and bore grooves provide hydrostatic thrust duringrotation of the rotor. Various embodiments include the bore groove, theperipheral grooves, or both.

FIG. 10 illustrates another embodiment of the rotor. Rotor 1000 includesa bore 1010, a non-bladed portion 1030, and a plurality of pumpingblades 1020. The rotor may have grooves 1050 within the bore. The rotorincludes paddles 1040 located at the periphery of the rotor. The paddles1040 are distinct from any pumping blades 1020. The grooved bore andperipheral paddles provide hydrostatic thrust during rotation of therotor. Various embodiments include the bore groove, the peripheralpaddles, or both.

Aside from any magnetic or hydrostatic bearings, the pump may include ahydrodynamic bearing as described with respect to FIGS. 1 and 4.Hydrodynamic bearings rely on the geometry and the relative motion oftwo surfaces to generate pressure. The rotor or the housing or both mayinclude features to support a hydrodynamic bearing. Various surfacegeometries suitable for hydrodynamic bearings include grooves andtapers. The groove or taper patterns and location of the grooves ortapers may be chosen to meet specific design constraints. In variousembodiments, one of the hydrodynamic surfaces has grooves arranged in aspiral or a spiral herringbone pattern.

Referring to FIG. 9, for example, the rotor may include features at itsperiphery to generate a radial hydrodynamic bearing. The radius of theperiphery of the non-bladed portion of the rotor 930, for example, mayvary in size to create a taper between the grooves. Referring to 970(a), the radial distances (R1, R2) measured from the center of the rotorto two different points along the periphery of the rotor between thegrooves is substantially the same such that R1=R2. Referring to 970 (b),the radial distances (R1, R2) measured from the center of the rotor totwo different points between the grooves of the rotor are substantiallydistinct. In one embodiment, R1<R2 to create a tapered outer peripherybetween the grooves.

FIGS. 11A and 11B illustrate embodiments of surface geometries suitablefor thrust or journal hydrodynamic bearings. The surface geometriescomprise groove patterns for axial (thrust) and radial (journal)hydrodynamic bearings. The groove patterns may be located on either therotor or on an associated portion of the housing (or spindle).

FIG. 11A illustrates a groove pattern for an axial hydrodynamic bearing.Although the groove pattern is illustrated as being disposed on thebottom of rotor 1100 (see, e.g., reference 124 of FIG. 1), the groovepattern may alternatively be located on the lower housing portion thatfaces the bottom of the rotor (see, e.g., reference 118 of FIG. 1).

Rotor 1100 includes a plurality of nested grooves. Grooves 1102 and1104, for example, form a curved groove pair that is “nested” withinanother groove pair 1106. The illustrated groove patterns may also bedescribed as a herringbone or spiraled herringbone pattern. When therotor rotates in the direction indicated, hydrodynamic thrust forces(i.e., orthogonal to the rotor base) are generated to push the bottom ofthe rotor away from the facing lower housing portion when the clearancebetween the bottom of the rotor and the lower housing portion fallsbelow a pre-determined threshold.

FIG. 11B illustrates one embodiment of a rotor bore cross-section 1150exhibiting a groove pattern suitable for a radial hydrodynamic bearingrelative to the rotor axis of rotation 1190. This groove pattern mayreside on the rotor bore surface as shown or on the periphery of therotor. Alternatively, the groove pattern may reside on the spindle or onthe wall of the pumping chamber (opposing the periphery of the rotor).As with the example of FIG. 11A, the grooves are nested. This pattern isreferred to as a herringbone groove. With respect to FIGS. 11A or 11B,the grooves may be chemically, thermally, or mechanically etched intothe surface they are disposed upon.

The grooved bore and peripheral grooves or paddles effectively generateauxiliary hydrostatic thrust forces that are applied to the backside ofthe rotor. These auxiliary hydrostatic axial forces supplement thehydrostatic forces generated by the impeller blades.

In various embodiments, the axial hydrostatic bearing may be combinedwith a radial hydrodynamic bearing as discussed with respect to FIGS. 1and 4. Referring to FIG. 9, the grooved bore 910 may support bothhydrodynamic journal bearing as well as an axial (thrust) hydrostaticbearing. Preferably, however, the bore is not relied upon for bothhydrodynamic journal and thrust bearings. Hydrostatic thrust andhydrodynamic journal bearings may, however, be combined at the peripheryof the rotor. Obviously, the rotors of FIGS. 8-9 have greatersuitability for the peripheral hydrodynamic bearing than the paddledrotor of FIG. 10.

FIG. 12 illustrates the pump 1210 operationally coupled to move aworking fluid 1240 from a source 1220 to a destination 1230. A firstworking fluid conduit 1222 couples the source to the pump inlet 1214. Asecond working fluid conduit 1232 couples the pump outlet 1216 to thedestination. The working fluid is the fluid moved by the pump from thesource to the destination. In a medical application, for example, theworking fluid might be blood. In one embodiment, the source anddestination are arteries such that the pump moves blood from one arteryto another artery.

Various “contactless” bearing mechanisms have been described asalternatives to mechanical contact bearings for rotary pumps. Inparticular, rotor, impeller, and housing design features are provided toachieve hydrodynamic, hydrostatic, or magnetic bearings. These designfeatures may be used in conjunction with each other, if desired.

In the preceding detailed description, the invention is described withreference to specific exemplary embodiments thereof. Variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the invention as set forth in the claims.The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

1. A pump apparatus comprising: a pump housing defining a pumpingchamber, the pump housing having a spindle extending from a wall of thepump housing into the pumping chamber, wherein the spindle has a steppedportion adjacent the wall serving to regulate hydrostatic forces duringoperation of said pump apparatus.
 2. The apparatus of claim 1 whereinthe stepped portion is defined by a change in spindle diameter.
 3. Theapparatus of claim 1 wherein at least one of the housing and the spindlehas a surface geometry suitable for supporting a hydrodynamic bearing.4. The apparatus of claim 3 wherein the surface geometry comprises aplurality of spiral grooves.
 5. The apparatus of claim 3 wherein thesurface geometry comprises a herringbone groove pattern.
 6. Theapparatus of claim 1 further comprising: a rotor configured to rotateabout the spindle, wherein the rotor further comprises paddles locatedat a periphery of the rotor to generate hydrostatic thrust forces, thepaddles distinct from any impeller blades.
 7. The apparatus of claim 6wherein the rotor further comprises a grooved bore for generatinghydrostatic thrust forces during rotation.
 8. The apparatus of claim 1further comprising: a rotor configured to rotate about the spindle,wherein the rotor further comprises grooves located at a periphery ofthe rotor, the grooves establishing hydrostatic thrust forces duringrotation of the rotor.
 9. The apparatus of claim 8 wherein the rotorfurther comprises a grooved bore for generating hydrostatic thrustforces during rotation.
 10. The apparatus of claim 1 further comprising:a rotor configured to rotate about the spindle, wherein a bore of therotor is grooved to generate hydrostatic thrust forces during rotation.11. The apparatus of claim 1 further comprising: a rotor configured torotate about the spindle, wherein at least one of the bore and theperiphery of the rotor includes a first set of grooves, wherein thefirst set of grooves establish hydrostatic thrust forces during rotationof the rotor, wherein at least one of the rotor, the spindle, and thehousing has a surface geometry suitable for supporting a hydrodynamicbearing.
 12. The apparatus of claim 11 wherein the surface geometrycomprises a plurality of spiral grooves.
 13. The apparatus of claim 11wherein the surface geometry comprises a herringbone groove pattern. 14.The apparatus of claim 11 further comprising: a rotor configured torotate about the spindle; and a plurality of drive magnets disposedwithin a non-bladed portion of the rotor.
 15. The pump apparatus as setforth in claim 1, further comprising a rotor and wherein said steppedportion regulates hydrostatic forces so as to control a position of saidrotor along a longitudinal axis of said spindle.